1. Field of the Invention
The present invention relates to a radiation-resistant non-halogen flame-retardant resin composition which can be used in an environment exposed to radiation such as a particle accelerator facility, nuclear power plant, or nuclear reprocessing facility. Furthermore, the present invention relates to an electric wire and cable that uses the resin composition.
2. Description of Related Art
Ionizing radiation including gamma rays is present in a beam line peripheral equipment in a particle accelerator facility, a nuclear power plant, a fast breeder reactor, and a nuclear reprocessing facility. For this reason, electric wires and cables used to supply electric power or transmit signals to these sites must withstand deterioration due to ionizing radiation (see, e.g., JP-A Hei 7 (1995)-179682 and JP-A Hei 1 (1989)-128313).
From the viewpoints of safety in case of a fire and protection of environments, electric wires and cables have been required to be non-halogen electric wires and cables which do not include halogen elements including chlorine and nor do they generate harmful gases when they are burnt (see, e.g., JP-A-2002-302574, JP-A-2001-345022, WO2003-046085, JP-A-2000-281837, and JP-A Hei 5 (1993)-81936). In response to this requirement, electric wires and cables covered with flame-retardant materials, which are stipulated in JIS C 3605 and JIS C 3401, have been widely used in buildings in recent years. Here, it means that flame-retardant materials are non-halogen resin compositions produced by blending soft ethylene polymer such as ethylene ethyl acrylate (EEA), ethylene-vinyl acetate (EVA) copolymer, or ethylene α-olefin copolymer with a metal hydroxide-based flame retardant such as magnesium hydroxide.
However, the main component of the resin composition used for the above electric wires and cables covered with flame-retardant materials is ethylene polymer, as described above. When these electric wires and cables are exposed to ionizing radiation even at room temperature, they excessively deteriorate and cannot be used in a radiation environment typified by particle accelerator facilities and nuclear power facilities.
This is because ethylene polymer exposed to ionizing radiation undergoes oxidative deterioration and thereby main chain scission and cross linkage progress, significantly reducing flame retardancy and mechanical properties including elongation and tensile strength. Furthermore, when electrical wires and cables are deteriorated, their sheaths are prone to crack. Safety in case of a fire is lowered.